MORE DATA MODELLING CONCEPTS
Figure 4.1 is a copy of Figure 2.16, the final conceptual data model we developed when working through Chapter 2. This model only uses the basic data modelling concepts of entity, attribute and relationship. For many purposes these are sufficient, but there are two further concepts that will definitely be needed in the development of a corporate data model and may be useful when modelling at the project level:
entity subtypes;
the specification that two or more relationships are mutually exclusive.
FIGURE 4.1 The human resources conceptual data model developed in Chapter 2
Entity subtypes
Entity subtyping is a ...
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